I have the new 07 2500HD with 6.0L 6sp and 4.10 rear end. I tow a 6000lb TT. Here in the PNW I am always going uphill so the 4.10's were a given. I am only at 1/2 the tow rating for the truck and it handles the TT like it isn't even back there. I rarely need to drop below 4th gear for any hy grade and can easily maintain 55-60 in 4th turning 3500-4000 RPM (which is the sweet spot for that engine).60MPH is around 1900RPM and on the flat I can cruise on the level with no problems. I get an average of 13MPG light and around 10-11 towing. The other thing to look at is the wheels and tires - if you have oversized tires and wheels - you reduce the effective torque to the wheels.
A 3.73 rear end will reduce the RPMs by 20% which will drop you back down the torque curve for the engine. If you are not towing or hauling it would be OK and would improve the MPG for the truck solo - but would probably require using the next gear down to get into the sweet spots. The key to good MPG when towing is to keep the engine running in that sweet spot. The gearing of the 6sp is best suited for the 4.10 rear end
07 Chevy 2500HD 6.0L ,6 speed auto, 4x4, Blue Granite Metalic
05 Arctic Fox 22H